Microphone



March 5, 192 9. L. L. NETTLETON MICROPHONE 2 Sheets-Sheet M a ATTORNEY NW M. l

INVENTOR.

Fil ed Aug. 20, 1925 March 5, 1929- L. L. NETTLIETON MICROPHONE Filed Aug. 20, 1925 2 Sheets-Sheet RM WW $5 N w v INVENTOR i x m,

ATTORNEY I Patented Mar. 5, 1929.

UNlTE DQSTATES PATENT OFFICE.

Lewis L. NETTLETON, or wfLKINsBUnG, PENNSYLVANIA, AssrGNoR TO THE uNIoN.

SWITCH & SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

MICROPHONE.

-Application filed August 20, 1925. Serial No. 51,403.

My invention relatesto electrical microphones. I I will describe several forms of microphones embodying my invention, and will then point out the novel features thereof in claims. The present application is a continuation of my co-pending application,' Serial No. 744,644, filed October 20, 1924,. for microphones, in so far as the subject matter common to the two is concerned. I

In theaccompanying drawing, Fig. 1 is a view in front elevation showing one form of microphone embodying my invention. Fig. 2 is a vertical sectional view on the line lI--.ll of Fig. 1 looking in the direction indicated by the arrows. Fig. 3 is a frontview showing a modified form of microphone also embodying my invention. Fig. 4 is sectional view on the line Ill-JV of Fig. 3 looking in the direction indicated by the arrows. Fig. 5 is a'detail view showing on an e n-, larged scale a portion of the microphones 11- lustrated in Figs. 1 and: 3. Fig. 6 is a view showing a modified arrangement of the electrical connections shown in Fig. 2. Fig. 7

V is a sectional view showing'another modilied form of microphone embodying my invention.

Similar reference characters refer to similar parts in each of the several views.

Referring first to Figs. 1 and 2, the microphone in the form here shown comprises a block A containing two microphone unitsv U and U ,;which units arelocated in two 1 circular holes D. The two units are exactly with a shoulder 3 having therein a numberalike" and consequently a description ofone unit will apply equally well to the other.

Referring to unit U, the hole D is provided with a sleeve E of insulating material in which is inserted a bushing G of insulating material. Threaded into bushing G is a stem J, the inner end of which forms a .plunger 7 which is located in-the sleeve E. The plunger 7 may be" adjusted to the desired position by turning the stem J inthe bushing Gr,--and may .belOckedin adjustedposition by means Q1; a nut K located on the outside of the bushlng G.

The front face of the block A-is provided of grooves 5. Two fiat strips 4 and "4 of elastic material such as' spring steel extend across the faceof the block A and intersect 'at substantially right angles at a point which is in the axis of the sleeve E. The ends of the strips 4 and 4 "are rigidly fastened to the shoulder 3 of block A by means of clamps B which are attached'to the block by means of screws 1. Attached to the strips 4 and {P by a screw 17 at the point where the strips intersect is a piston N which projects into the sleeve-E and is spaced from the plunger 7. This piston is slightly less in diameter than the inside of the sleeve E so that the piston is free to vibrate within the sleeve.

A second strip 4? of spring steel is attached to the block A by clamps B and intersects the strip 4 at a point which is in the axis in the pressure thereon by piston N in the usual and well known manner.

In order to regulate the tension of strip 4 I provide two clamps C the inner sides of which are rounded to conform with the con- 7 tour of the grooves 5. These clamps are drawn into the grooves by screws 6 so that they force the strip 4 into the grooves and thus increase the tension on the strip as the screws are turned up. vThistension adjustment feature is shown more clearly in Fig. 5' than in Fig. 2. The strips 4 and 4 are adjusted as to tension in the same manner as strip 4.

"The pistons N mayfbe vibrated by any suitable means. As here shown vibration of these pistons is caused by an electromagnet L provided with an armature 13 which is carried by 'a block 14, and this block 14 is in turn connected with the two pistons N by a truss M. When alternating current is applied to the electromagnet L, the two' pistonsN are caused to vibrate in unison. v

- The two units U andU may be included in series or in multiple-in the output circuit.

ios

As shown inFig. 2 these units are connected in series in a circuit which'includes wires ternating current in the electromagnct L will cause variations of the current from battery 18 in the output circuit and so will cause alternating current to flow in the stator winding 20 of relay R.

As shown in Fig. 6 the two units U and U are connected in multiple in the circuit which includes battery 18 and primary l9;

nected in series, the voltage of the battery 18 may be higher than when a single unit is used. When the two units are connected in multiple themicrophone as a whole is more stable in operation than when a single unit is employed. With either arrangement of connections I have found that the power outputof the microphone is double when two units are employed instead of one.

Referring now to Figs. 3 and 4, the microphone here shown contains but a single unit, and is arranged to use a stack of thin carbon disks instead of the mass of granules shown in Fig. 2. The microphone comprises a block A carrying a supporting member I which is attached to the block by screws 16 and is provided at its upper end with a threaded aperture to receive a threaded post Q extending into the hole D in the block A The inner end of post Q is provided with an insulated sleeve E which sleeve is surrounded by a stack of thin carbon disks 24. These disks rest a ainst the stop 25 which screws on to the post E2, and is locked in adjusted position thereon by a nut 26. The post Q is in turn locked in adjusted position in respect to the support P by means of nuts 10 and 11. In

this form the front face of block A is round,

so that the shoulder, which is here designated 3 is annular in shape and the groove 5 is likewise annular. The strips 4 and 4 are attached to the block A by a single ring B, and are adjusted as to tension by clamps G which co-operate with the groove 5. The vibrating member or piston, which is here designated-N is attached to the strips 4 and 4 by a screw. 17 as in Fig. 1, and is provided .with a central recess 27 to receive the inner end of the post Q. This piston bears against the disks 24 so that these disks are held between the piston N and the stop 25. The piston N may be operated by an electromagnet. or other suitable device through the medium of a rod M and the microphone may be connected in an electrical circuit by means of wires 8 and '9.

The following discussion applies to each i unit U and U? in Figs. 1 and 2 also to the single unit shown in 3.

One advantage of my invention is that the tension of the strips 4, 4 and 4*, and hence the amount of the restoring force, may be accurately, conveniently and permanently adjusted.

Piston N, or piston N is normally held in an intermediate position wherein the forces acting on the moving parts are in cqnilibrium; these forces being due to the stiffness of the strips 4, 4, and 4", and the tension applied to these strips. The piston has, therefore, but one intermediate position of rest. In this respect, a microphone embodying my invention is an improvement over micro- I, phones of the type comprising a circular disk When the two microphone units are condiaphragm fixed at its edge, a diaphragm of the latter type being capable of assuming at least two difi'ercnt positions of rest. A further advantage of my invention over 1nicrophones having a disk diaphragm is that with the intersecting fiat strips :1 more flexible and more sensitive vibrating system is possible because it is only necessary to apply a comparatively small tension to the strips.

If the strips 4, 4 and 4" are placed under a comparatively small tension, the force tending to restore the vibrating system to its position of rest, when the system is moved out of this position, is largely due to the stitfness of the strips and is roughly proportioned to the displacement of the strips. If, however, the strips are subjected to considerable stretch, or tension, the restoring force is due largely to the elasticity of the strips and is then approximately proportioned to the cube of the displacement. By varying thetension of the strips, therefore, I canregulate the variations in the restoring force with displacement for a given strip between-wide limits. This feature is an advantage because it is usually desirable for the vibrating system to be biased to its position of rest by a force which varies according to the same law as does the force which drives 'this system.

With my invention I can, by properly choosim the dimensions of the stri s, and by properl y regulating the tension 0 the strips, provlde any reasonable variations in the restority of auxiliary clamps C, the inner ends of H which are rounded to conform with the contour of the annular groove 5. A threaded rod M is attached to the strips 4 and 4 Where these strips intersect, the attachment being accomplished by a pair of nuts 42 and42".

The rod M may bevibrated by any suitable means, such, for example, as the magnet L and armature 13, shown in Fig. 2.

The shell A contains a plurality of cells, F, F and F As here shown, each cell is made up of a hollow cylindrical member 31 of insulating materialand a pair of end plates 30 and 32 of electro-conducting material, the end plates 32 and 30 of adjacent cells being separated by a disk 33 of insulating material. The plate 30 at the left-hand end of cellF is electrically insulated from the flange 28 of the shell A by a disk 29 of insulating material. The elements making up the three microphone units are compressed and held firmly in place by a cap 38 which screws onto the flanged and threaded rear face of the shell A The rlght-hand conducting plate 32 of the cell F is electrically separated from the cap 38 by a disk 29 of insulating material. The elements making up the several units are preferably surrounded by a sleeve 41 of insulating material, which in turn is surrounded by a sleeve or tube 40 of metal.

The rod M extends through holes in the plates and disks 29, 30, 32, 33, and 29 and is 7 provided with plungers or pistons H H and H which are located in the cells, F, F and F ,-respectively. These pistons are spaced by sleeves 43 of insulating material surrounding the rod M Each cell is packed with granular carbon 49, so that the granules are in electrical contact with the piston H and with the two plates 30 and 32 forming the end walls of the cell. It will be seen, therefore, that when the rod M is moved toward the right, the carbon granules on the right of the piston in each cell are compressed, whereas the pressure on the carbon granules to the left of the piston in each cell is reduced. When the rod M moves toward the left, the reverse operation occurs. llt follows that each cell comprises two microphone relays.

Recesses 35 are cut in the sleeves 40, 41 and 31 to accommodate contact fingers 36 3.116.137, which contact fingers are suitably mounted in the shell A so that each finger 36 engages with an end plate 30, and each finger 37 engages with an end plate 32.

The microphone shown in Fig. 7 may be used. with any suitable arrangement of electrical connections. As here shown, it is so connected as to form a part of a push-pull amplifier. The three contact fingers 36 age connected by the conductor 47 with one' te minal of the primary 45 of a transformer T, whereas the three contact fingers 37 are connected by a conductor 48 with the other terminal of the primary 45. One terminal of a battery 46 is connected with the rod M and so with each of the pistons H H? and H the other terminal of the battery 46 being con nected with the middle point of the trans-- ing the ends of said former primary 45. The effects of the several mlcrophcne units are thus made cumulative to create in the secondary 44 of trans- It will, of course, be understood that the clearance between the insulating sleeves 43 and the cell partitions, and also the clearance between the pistons H and the sleeves 31, are sufiicient to permit free vibration of the rod and pistons, but not sufiicient to permit the passage of the carbon granules.

Although I have herein shown and described only a few forms of microphones cmb'odying my invention, it is understood that .various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, I claim is: 2

what

1. A microphone" comprising a flat strip of elastic material, means for rigidly supportstrip, other means for varying the tension of said strip, and a vibratable member attached to said strip adjacent the center thereof.

2. A microphone comprising a rigid block having a central aperture, a fiat strip of elas tic material, means for rigidly clamping the ends of said strip to said block leaving the middle portion of the strip free to vibrate,

' means for varying the. tension of said strip,

and a vibratable member in said aperture attached to said strip adjacent the center of said aperture.

3. A microphone comprising two flat strips of elastic material disposed in substantially the same plane and one strip intersecting the other atan angle near themiddle of each strip, means for rigidly supporting the ends of each strip, means for varying the tension of each strip, and a vibratable member attached to said strips adjacenttheir point of intersection.

4. In a microphone, a vibratable member, and means for supporting said member comprising a flat strip of elastic material rigidly supported at its ends, and means for controlling the natural period of'said strip by varying the tension-thereof;

means for bratable member attached to said strips adjacent their point of intersection.

6. A microphone comprising two flat strips of elastic material intersecting at a point inforcing said strip into said groove to increase the tension of said strip, and a vibratable member attached to said strip intermediate the ends of the strip.

8. In combination, a rigid block having a substantially flat surface provided with a groove, two flat strips of elastic material extending entirely across. said groove and crossing substantiall at right angles, means for securing the en s of said strips to said block, separate means for forcing each strip into said groove intermediate the ends of the strips, and vibratable means attached to said strips adjacent the point of crossing thereof.

9. A microphone comprising a rigid block having an aperture, a plunger adjustably fixed in said aperture, two flat strips of elastic material crossed substantially at right angles, means for securing the ends of said strips to said block, means forvarying the tension of each strip,-a vibratable piston in said aperture and attached to said strips adjacent the'point of crossing thereof, and carbon granules in said aperture between said piston and said plunger.

10. A microphone comprising an elongated, flat comparatively thin strip of elastic material, means for rigidly supportingthe two ends of said strip, other means for controlling the tension of said strip, and a pressure responsive device comprising a vibratable member operativcly connected with said strip intermediate the ends of the strip.

11. A microphone comprising a vibratable body means eflective when said body is moved out of a position of rest to exert a restoring force upon the body to return the body to said position of rest, and adjusting means for regulating the variation of said force with respect to the displacement of said body.

7 In testimony whereof I afiix my signature.

' LEWlS L. NETTLETON. 

